Phase separation in wurtzite CuInxGa1−xS2 nanoparticles

It has earlier been reported that that the gallium incorporation in wurtzite CuInS2 (CIS) results in structural distortion, non-homogeneous shape, and distribution of particles. However, a detailed study of the effect of Ga substitution on the structure and morphology has not been reported. Here, we report the synthesis of nanocrystalline CuInxGa1−xS2 (x = 1, 0.7, 0.5, 0.3, and 0) wurtzite particles by solution processing in a nitrogen atmosphere. Structural analyses by X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the as-synthesized CuInS2 (CIS) and CuGaS2 (CGS) nanoparticle were single-phase wurtzite structures, whereas CuIn0.7Ga0.3S2, CuIn0.5Ga0.5S2, and CuIn0.3Ga0.7S2 had three wurtzite phases having In-rich, In–Ga, and Ga-rich compositions. The shape of the resulting nanoparticles was either elongated, polygonal, or tadpole depending on the phase composition. In-rich particles had elongated rod-like morphology, the In–Ga particles were irregular hexagonal/equiaxed, while the Ga-rich phase formed with a tadpole morphology. The bandgap of the wurtzite-CuInxGa1−xS2 increased with Ga substitution: from 1.49 eV for CIS to 2.0 eV for CGS.